In 2002 they interviewed 409 and 147 enrolled. I know they over accept b/c some will go to other schools but that is ~36%. I would imagine they would have to accept about 25%-30% above that in order to get the class size they want. So I would guess they accept about 60% of those who interview. This is only speculation.
When the director of admissions was at UW last week, I think she said that they have so far interviewed (o plan to, I'm not sure) 437 of 840 applicants and have so far accepted about 75 of a class of 150-160.